1. Field of the Invention
The present invention relates to a method for manufacturing a fuel inlet (fuel feed pipe) for feeding fuel such as gas to a fuel tank of a motor vehicle or the like.
2. Description of the Background Art
Conventionally, an inlet pipe which constitutes a fuel inlet has a shape in which one end of the pipe is eccentrically expanded so that a fuel feed nozzle can be inserted therein, a screw structure is formed in this expanded portion so that a cap can be attached thereto, and a seal portion is formed by curling the end of the expanded portion so as to prevent fuel from leaking between the inside surface of the cap. See, for example, Japanese Patent Application Publication 2000 334512 (‘D1’hereinafter).
The conventional fuel inlet in which a screw structure is formed in an expanded end portion has the following drawbacks:
The end portion becomes non-uniform in thickness or is partially extended in the course of the expanding process. If a screw structure is formed in such a non-uniform portion, the groove portion of the screw structure has an extremely thin thickness or is deformed.
The screw structure formed in the conventional fuel inlet often has a double-start thread structure so that a cap can be attached or removed quickly. The double-start thread structure is obtained by punch (cam-shaped) forming or roll forming as disclosed in the above-mentioned D1. As shown in FIG. 11(a), in a case where the groove portions of the screw structure are formed to overlap with respect to each other, the amount of the material is small in the overlapping area and the seal portion is partially dented in the axial direction. As shown in FIG. 11(b), in a case where the groove portions of the screw structure are formed apart with respect to each other, the amount of the material is large and the seal portion is extended in the axial direction. It might be possible to form the groove portions without overlapping or separating, however this is not always possible depending on the relation to the cap.